Transportation Planning Capacity Building Program
— Peer Exchange Report —
Using ACS Data in Transportation Planning Applications
Daytona Beach Florida
||May 10 — 11, 2007
American Association of State Highway and Transportation Officials
Florida Department of Transportation
Georgia Department of Transportation
Iowa Department of Transportation
New York State Department of Transportation
Virginia Department of Transportation
Wisconsin Department of Transportation
Minnesota Department of Transportation
Texas Department of Transportation
San Diego Association of Governments
Southeast Michigan Council of Governments
Association of Central Oklahoma Governments
Atlanta Regional Commission
Capital Region Council of Governments
Metropolitan Council Twin Cities
Metropolitan Transportation Commission
Volusia County Metropolitan Planning Organization
Houston-Galveston Area Council
Federal Highway Administration
Bureau of Transportation Statistics
Federal Transit Administration
Volpe National Transportation Systems Center
Louis Berger Group
Texas Transportation Institute
University of Iowa
University of South Florida, Center for Urban Transportation Research
This report summarizes the presentations and discussions at a Peer Exchange held through the FHWA/FTA Transportation Planning Capacity Building (TPCB) Program. The peer exchange was organized by the American Association of State Highway and Transportation Officials (AASHTO) Standing Committee on Planning (SCOP) Census Data Workgroup chaired by Jonette Kreideweis (Minnesota DOT). Attendees were from AASHTO, state departments of transportation, metropolitan planning organizations and councils of government, universities, Census Bureau, the United States Department of Transportation, and the private sector. Following the keynote addresses, issue-specific sessions were held in which multiple presenters gave short presentations and all participants joined in discussion. Twenty—one presentations are posted at ftp://ftp.camsys.com/clientsupport/CTPPdata/Daytona_peer/
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Transportation planners and analysts are making or contemplating a transition from using data from the decennial Census "long form" to the new American Community Survey (ACS). The Census Bureau released the first round of data from the 2005 ACS in the fall of 2006. In October 2006, the AASHTO SCOP Census Data Workgroup secured support for continuing the Census Transportation Planning Products (CTPP) concept using a consolidated purchase. The Peer Exchange presented an opportunity to share emerging practices and discuss issues and challenges in applying and integrating ACS data into transportation planning activities. States, MPOs and universities are independently beginning to use the ACS data and develop analytic tools using the ACS The Peer Exchange provided a platform for sharing information, documenting practices and issues, discussing plans for the future CTPP, and exploring how to help inform the larger transportation planning community.
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III. Key Findings from the Peer Exchange
There is a Strong Demand for Transportation Data Products from ACS
The CTPP 2000 is widely used in the transportation planning community and beyond. Distinguishing characteristics are that the sample size is large (relative to local surveys), response rates are high due to the requirements to participate in the census, and it is one of the best sources for trip distribution data (data on the origins and destination of work trips). The national availability of the CTPP 2000 enables professionals to become familiar with it and use it in various locations. As a nationally collected data source it has the benefit of having high credibility and professional oversight in its development and supporting resource and training materials. To date, once the States and MPOs paid for CTPP, there have not been additional fees charge to other users. This has enabled local planners to avoid the time and cost of new primary data collection.
There is Strong Support for Transportation Data Products from ACS
For the reasons cited above, there is strong interest in having a CTPP product from (or using) the ACS. While the sample size will be different there remains a desire to have this standardized national resource to support transportation planning. States, MPOs and universities are independently beginning to use the ACS data and develop analytic tools that rely on ACS. The Peer Exchange provided a platform for sharing information, documenting practices and issues, discussing plans for the future data products.
Uncertainty has Surrounded Transportation Data Products from ACS
Several factors have collectively resulted in a great deal of uncertainty in the planning community regarding the ACS and the prospect of transportation data tabulated from it. These uncertainties have been exacerbated by larger uncertainties regarding several federal level data collection initiatives. Funding for the ACS has regularly been uncertain clouding expectations. In addition, funding for the next National Household Travel Survey (NHTS) has been uncertain. Thus, practitioners have been faced with a confusing and unsettling picture regarding the availability of transportation planning data from federal sources and the ability to validate, fuse, merge, or substitute various data resources as details on their timing, quality and features evolve.
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Understanding the American Community Survey
The planning profession is in the early stages of understanding the nature of the potential applications of the ACS. Some of the uncertainty is simply due to busy professionals not yet being aware while other uncertainty stems from limited disclosure or dissemination of important aspects of the planned future data products. Other issues involve the release and usability of the data. To date, the only data released has been for areas with 65,000 residents or more. This has left many areas with partial data and planners left 'waiting" for the rest of the data. Remaining questions include:
- Release schedules for ACS products for various geographic scales
- How multiyear data items will be developed including how group quarters will be treated
- How ACS data uses and can be used with population estimates at the sub county level
- How to treat standard errors when discerning and communicating ACS findings
- Understanding income differences between ACS and Census or other sources
- Understanding how and when the 2010 census will be reflected in ACS products
- How geographies for reporting will be updated
- Understanding how rounding and suppression will be applied and impact products
- Understanding the impact of data collection over twelve months instead of a point in time
ACS as a Source of Zone-to-Zone Flow Data
One of the unique characteristics of the CTPP 2000 was its value for understanding local work trip distribution. This application has no readily available alternative data source. Trip distribution is relatively stable over time thus enabling older CTPP data to retain value. Flow data is fundamental to calibrating regional models so has relevance to roadway and transit modes for major regional and corridor planning. Sample sizes for local survey are too small to substitute for this purpose. The smaller ACS sample and data suppression raise concerns about the availability of flow data for smaller geographies. The zone to zone flow tables, preferably by mode, provide the greatest challenge for survey data in terms of ensuring adequate sample size.
One potential alternative worth examination for small area home-to-work flow data is the Longitudinal Employer-Household Dynamics (LEHD) On-The-Map data produced being developed by the U.S. Census Bureau and funded by the US Department of Labor. This project synthesizes "home-to-work" flows using federal and State administrative records. The potential for fusing LEHD On-The-Map data with ACS data that includes travel mode and time and other household characteristics could be used to develop a richer understanding of trip distribution. This might enable analysts to better understand and model home to work distributions thus reducing the need for location specific zone flow data on a recurring basis.
ACS and Transit
Transit is fundamentally different than the auto mode. It is typically involves a walk access/egress mode and thus significantly benefits from small scale geographies for planning data. Also, since transit use is modest, it requires a very larger general population sample to produce a sufficient number of transit passenger responses. These traits influence the transit applications of ACS, as well as the applications for bike and walk modes. As small area ACS data becomes available there may be more use by transit planners. Transit continues to benefit from the role of ACS data in regional and corridor model validation/calibration for major investment studies and ACS may be of future value in updating zonal socio-demographic characteristics that can support service planning. The ACS also supports general policy research and planning that can impact transit. The annual updating of the data can benefit transit particularly in dynamic fast growth/change areas. The ACS use of the "usual mode" versus "actual mode" requires caution when using the ACS transit mode data.
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Through the course of the exchange a variety of questions arose regarding numerous aspects of the ACS and future CTPP data products. The diverse conference participation list exemplified one of the challenges of producing, refining, disseminating ACS data products and research. Building the CTPP around the ACS is a collaborative initiative with a broad base of participants that exemplifies the value of these products; however, this array of participants also clouds the responsibilities and creates uncertainty regarding roles and responsibilities. This, combined with other uncertainties referenced previously, has left most users with a very modest level of understanding of what products, training, research, and other resources will be available to support their application of ACS and any CTPP data products. Absent a clear institutional or legislative mandate, initiatives of concerned individuals and institutions in a somewhat ad hoc fashion have been responsible for the very important progress to date. While this partnership arrangement may be a necessary feature going forward, efforts to define roles and responsibilities and to communicate what is being done will be of great value to the user community as we continue through this transitional period. Communications strategies, outreach mechanisms, training priorities, scheduling release dates, opportunities for input, redefining geography, and developing consensus on data formats are all issues that will benefit from collaborative input but will also benefit from coordinated communications amongst entities.
This situation clearly highlights the need for an ongoing partnership commitment from the states, MPOs, regions, US DOT and AASHTO. This partnership should serve as the forum for coordination of actions and decisions and as a means of assuring communications between the partners.
Evolution of ACS and Integration with Other Data Sources